Yes, the historical conjecture is more than coincidence but that alone does not make a proof. However, I think that it will be a celestial event that somehow impacts (no pun intended) Earth.

Most if not all of the celestial computers or charts, such as Stonehenge or the Mayan "calendar" are mistaken for cult artifacts or for calendars when in fact they were constructed for a radically different purpose. The purpose is deeply cultural and is therefore inaccessible to us in this modern world.

The Druids didn't really need to know the date of the year. If all you want is to keep track of the date, just write it down on parchment. They did need to know the seasons and perturbations of the known celestial bodies, including eclipses of the sun and moon.